Doors are often hung using concealed bearing hinges. A typical concealed bearing hinge comprises two hinge leaves, one attached to the door and the other attached to a door jamb such as shown in U.S. Pat No. 3,499,183 to Parsons. Between the two hinge leaves of a typical concealed bearing hinge there is generally a three knuckle barrel, the top and bottom knuckles of which are connected to one of the hinge leaves and the middle knuckle of which is connected to the other hinge leaf. One of the hinge leaves is generally attached with screws to the door and the other hinge leaf is generally attached with screws to the jamb on which the door is hung.
In recent years, some building codes have required new structures, for example, apartment houses, to include door closing devices on the entrance door of each housing unit. While in higher income units concealed hydraulic closers have been utilized, the requirements of the building codes can be satisfied by less expensive spring hinges.
Heretofore, spring hinges have been developed which meet the requirements of the building codes. A spring hinge is a hinge having within its tubular section a torsion spring which urges the door into a closed position. Prior spring hinges have been manufactured with knuckles of large diameter and excessive length, often longer than the leaves, to accommodate a spring sufficiently strong to provide the necessary torque for closing the door. Such hinges have a bulky and unattractive appearance wholly unlike that of concealed bearing hinges or other aesthetically pleasing hinges. Thus, although it has been permissible, under the building codes, to use a bulky spring hinge in conjunction with a concealed bearing hinge, such an arrangement has not generally been accepted for aesthetic reasons. In particular, the reluctance to use the prior spring hinges in combination with a concealed bearing hinge is due primarily to the fact that such prior spring hinges have had an appearance, described above, which differs considerably from that of conventional concealed bearing hinges. Thus, if concealed bearing hinges are deemed desirable for aesthetic reasons, a concealed hydraulic door closer must be utilized. On the other hand, if spring hinges are deemed desirable for economic reasons, aesthetics may require that all hinges must be the unattractive bulky spring hinges because of the difference in appearance between them and the concealed bearing hinges.
Conventional two knuckle hinges comprise a pair of knuckles of equal length. If such conventional two knuckle hinges are transformed into a spring hinge, the maximum length of the spring is equal to the length of a knuckle or one half of the total barrel length. This restriction on the length of the spring prevents the use of springs that deliver the requisite torque and spring life. Accordingly, it is imperative that a spring hinge utilize a spring which is long enough to provide adequate torque without impairing either the performance or reliability of the spring.